1. Field of the Invention
This invention relates to electronic article surveillance (EAS) systems and more particularly to an EAS antenna system adapted for environments having wide exits and entrances.
2. Description of the Related Art
Electronic Article Surveillance (EAS) systems are detection systems that allow the identification of a marker or tag within a given detection region. EAS systems have many uses, but most often they are used as security systems for preventing shoplifting in stores or removal of property in office buildings. EAS systems come in many different forms and make use of a number of different technologies.
A typical EAS system includes an electronic detection unit, markers and/or tags, and a detacher or deactivator. The detection units can, for example, be formed as pedestal units, buried under floors, mounted on walls, or hung from ceilings. The detection units are usually placed in high traffic areas, such as entrances and exits of stores or office buildings. The markers and/or tags have special characteristics and are specifically designed to be affixed to or embedded in merchandise or other objects sought to be protected. When an active marker passes through a marker detection region, the EAS system sounds an alarm, a light is activated, and/or some other suitable alert devices are activated to indicate the removal of the marker from the prescribed area.
Common EAS systems operate with these same general principles using either transceivers, which each transmit and receive, or a separate transmitter and receiver. Typically the transmitter is placed on one side of the detection region and the receiver is placed on the opposite side of the detection region. The transmitter produces a predetermined excitation signal in a marker detection region. In the case of a retail store, this detection region is usually formed at a checkout aisle or an exit. When an EAS marker enters the detection region, the marker has a characteristic response to the excitation signal, which can be detected. For example, the marker may respond to the signal sent by the transmitter by using a simple semiconductor junction, a tuned circuit composed of an inductor and capacitor, soft magnetic strips or wires, or vibrating resonators. The receiver subsequently detects this characteristic response. By design, the characteristic response of the marker is distinctive and not likely to be created by natural circumstances.
EAS systems are often called upon for coverage of a large detection area, such as a wide mall store entrance. The mall store entrance can sometimes cover the width of the mall store itself. Such relatively large detection areas require special design considerations. For example, the EAS system used for coverage must be carefully designed to avoid any gaps through which a marker might pass through undetected, while simultaneously avoiding false alarming caused by markers attached to store inventory which may be displayed near the detection region.
When conventional EAS antenna systems, typically formed of loop antennas, are used in openings wider than about 2.5 meters, detection performance begins to deteriorate. Wide mall store entrances may need detection areas up to 4 to 5 meters wide, or wider. As used herein, wide exits and wide entrances refer to exits/entrances having widths greater than about 2.5 meters, and which are typically 4 to 5 meters or wider. Attempts at solutions to the wide entrance environment include adding additional antennas in the floor and/or ceiling. Adding loop antennas in existing flooring causes many problems, as the floor must be torn up in order to install the loop antenna.
U.S. Pat. No. 6,400,273 discloses an example of a wide exit solution that includes additional floor and ceiling mounted antennas. A large loop transmit antenna is mounted either in the floor or the ceiling, and several large ferrite core receiver antennas are mounted in the floor or ceiling. As known in the art, loop pedestal antennas can also be mounted at the ends of the detection zone, but are limited in range and cannot cover a wide exit. Multiple antennas can be spaced apart with overlapping detection zones to cover a wide area. The floor and ceiling mounted loop transmit antenna and ferrite core receiver antennas have serious installation requirements because of their size.